Scientists in New Zealand have found preliminary evidence that simple sugars like glucose can impair cognitive performance. Their double-blind, placebo-controlled study found that glucose-containing sweeteners were linked to reduced attention and response times.

“I am fascinated by how our senses influence our behaviour and affect our everyday lives,” said study author Mei Peng, a lecturer in sensory science at the University of Otago. “In particular, how sugar consumption might change the way our brains work. In the case of sweetness perception, we have evolved to favour this taste.”

Previous research on glucose ingestion has linked it to improved memory performance. But studies that examined the effect of glucose on other cognitive processes have led to mixed results.

In the latest study, 49 individuals consumed sweetened drinks containing either glucose, sucrose (table sugar), fructose (fruit sugar), or sucralose (an artificial sweetener) before completing three cognitive tests. The three tests consisted of a simple response time task, a measure of arithmetic processing, and the Stroop task.

The researchers also measured the participants’ blood glucose levels during the testing.

They found that participants who had consumed glucose or sucrose tended to perform worse on the cognitive tests than those who had consumed fructose or sucralose.

The human body converts sucrose into glucose and fructose. But unlike glucose, fructose does not traverse the blood-brain barrier.

“Our study suggests that the ‘sugar coma’ – with regards to glucose – is indeed a real phenomenon, where levels of attention seem to decline after consumption of glucose-containing sugar,” Peng told PsyPost.

This effect was amplified among participants who had fasted for 10-hours prior to the study.

“While the sample size is relatively small, the effect we observe is substantial,” Peng told PsyPost. “Future research should further quantify how different brain regions change after sugar consumption – by using neuroimaging techniques. This will help us better understand how attention deficits arise after glucose consumption.”

“As food is becoming increasingly diverse, accessible and delicious, it is important to conduct more research in this area to understand food choices and eating behaviours,” she added.